The present invention relates to a powder distributor for very accurately dosing a powder followed by the conveying thereof to a random use apparatus, such as a hot spray gun.
The hot spray guns to which the invention can be advantageously applied are in particular chemical flame torches and quenched arc plasma torch guns, in a free or a controlled atmosphere. However, the invention is not limited to these applications and can be used in all cases where it is necessary to dose and convey a bulk powder very accurately towards a random apparatus. In general terms, the powder distributors must fulfil the two essential functions of dosing the powder and conveying it up to the use apparatus.
In order to dose the powder, as far as possible account must be taken on the one hand of the need of being able to supply the powder use apparatus with powders having very different characteristics and on the other hand of the need of having a powder distributor ensuring that the use apparatus can be supplied with powder in a time-reproducible manner. Among the powder characteristics which must be modifiable, reference is particularly made to the nature of the powder (metallic, organic, ceramic, ceramel, oxide, etc.), its density (varying e.g. from 1 to 7), its grain size (varying e.g. between 2 and 200 microns), and the shape of the grains.
In the present state of the art, no powder distributor makes it possible to dose powder whilst completely satisfying these two requirements.
Thus, there are powder distributors, like that described in French Patent No. 2,048,781, in which the dosing of the powder is carried out by entirely fluidic means. Although such devices can be generally used for powders having very variable characteristics, they are not satisfactory from the standpoint of the time reproducibility of the results obtained.
Conversely, German Patent No. 2,807,866 describes powder distributors using entirely mechanical dosing means. However, these distributors adapt only poorly to the changes in the characteristics of the powder generally required by the user. Moreover, the presently existing dosing mechanisms do not make it possible to prevent the formation of powder accumulations and consequently the formation of arches stopping the advance of the product. Moreover, they do not make it possible to regulate the dosing of the powder as satisfactorily as is desirable and do not prevent possible grain size segregation. Moreover, existing powder distributors almost all use carrier gas for conveying the powder up to the use apparatus.